DESCRIPTION (Investigator's Abstract): The applicants' goal is to identify the mechanisms responsible for activity-dependent interocular competition and retinotopic map refinement during vertebrate visual development. Evidence, from studies of the developing retinotectal system, suggests that the N-methyl-D-aspartate (NMDA) subtype of excitatory amino acid (EAA) receptor is centrally involved in these processes. This proposal seeks to explore the interactions through which NMDA receptor activity mediates this activity-dependent synaptogenesis. The applicants' findings should be important in the development of clinical treatments or the prevention of amblyopia and for understanding environmental effects on brain development in general. Chronic treatment of doubly innervated "striped" tectal lobes with agonists and antagonists of cholinergic receptor systems and of the metabotropic EAA receptor will be sued to determine if these other transmitter systems modulate the function of the NMDA receptor in the tectum. The cellular sites of action and immediate structural effects of EAA or cholinergic receptor activation on retinal axons and tectal neurons will be explored using focal application of NMDA and cholinergic agonists and antagonists in a recently developed tissue culture system where the structural and Ca++ responses of retinal axons or dissociated tectal neurons can be studied in isolation or after they have made contact with each other. Time-lapse video analysis, image processing, stimulation of retinal action potentials and Ca++ imaging will be used in these studies. The applicants will also explore the complex excitatory and inhibitory circuitry of the tectum that is involved in mediating NMDA receptor effects using a tectal slice preparation and whole cell provided preliminary evidence that both NMDA and non-NMDA mediated excitatory synaptic currents and inhibitory shunting of these currents are induced in single tectal neurons by electrical stimulation of the optic tract. Finally, the applicants will begin to identify the biochemical components of the signalling systems through which synapses effective in opening NMDA channels are structurally stabilized using one and two dimensional gel analyses of protein changes in tecta acutely or chronically treated to drive NMDA receptors. Significantly altered proteins will be identified using antibody reagents that are either obtained from other labs or raised in the applicants laboratory using hybridomas produced from mice inocuated with the relevant protein bands from preparative gels.